1. Field of the Invention
The present invention relates to a stereoscopic map display, and more specifically, the present invention relates to a stereoscopic map display apparatus and method for an on-vehicle navigation apparatus, for displaying a map on a display apparatus and thereby guiding the vehicle to a destination.
2. Description of the Related Art
An on-vehicle navigation apparatus includes a map data storage device, such as a DVD-ROM, on which map data is stored, a display apparatus, and a vehicle movement detection apparatus, such as a gyro, a GPS (Global Positioning System) receiver, and a speed sensor, for detecting the current position and the current direction of the vehicle. In the on-vehicle navigation system, map data relating to the current position of the vehicle is read from the map data storage device, a map image of the area surrounding the current position of the vehicle is drawn based on the map data with a vehicle position mark superimposed thereon, and the map image is scrolled in accordance with the movement of the vehicle or the vehicle position mark is moved while the map image is fixed on the screen, so that the current travel location of the vehicle can be recognized at a glance.
Furthermore, the on-vehicle navigation apparatus typically includes a navigation function which allows the user to readily travel to a desired destination without taking the wrong roads. The navigation function automatically searches for the route with the lowest cost from a starting point to a destination based on the map data by performing simulations according to the breadth-first search method, Dijkstra method, etc., and stores the route as a navigation route. In operation, for example, the navigation route is displayed in a different color and in a thicker line compared with other roads on the map image, and when the vehicle comes within a predetermined distance of an intersection at which the vehicle must change its direction on the navigation route, an arrow indicating the new direction is drawn at the intersection on the map image, thereby guiding the user to the destination.
The cost refers to a value indicating the suitability as the navigation route, for example, the distance multiplied by constants in accordance with the road width, road type (ordinary road or highway, etc.), number of right turns and left turns, the predicted travel time of the vehicle, etc. The cost may differ for two different routes with the same distance if the user specifies, for example, whether or not to use toll roads, giving priority to minimize distance or time, etc.
The maps stored in the map data storage apparatus, such as the DVD-ROM, are segmented by appropriate longitudinal intervals and latitudinal intervals in accordance with various scales, for example, {fraction (1/12,500)}, {fraction (1/25,000)}, {fraction (1/50,000)}, and {fraction (1/100,000)}, and roads, etc. are stored as groups of coordinate values of nodes represented by the longitude and latitude thereof. A road consists of the connection between two or more nodes, and a connection between two nodes is referred to as a link. The map data includes (1) a road layer including a road list, a node table, an intersection node list, etc; (2) a background layer for displaying roads, buildings, parks, rivers, etc. on the map image; and (3) a character and symbol layer for displaying text such as administrative district names such as municipal names, names of roads, names of intersections, names of buildings, map symbols, etc.
Recently, the DVD-ROM may store, in addition to the map data, what is called townpage information, i.e., information regarding shops, companies, public facilities, etc. (category, address, phone number, etc.). The townpage information readily allows the user to search for a desired shop, etc.
One map display method for an on-vehicle navigation apparatus is a 3-D display in which the map is displayed stereoscopically. In the 3-D display, buildings and roads are displayed stereoscopically as if the vehicle were actually traveling through a crowd of buildings.
According to the 3-D display in a conventional navigation apparatus, however, shorter buildings and roads are hidden behind taller buildings, causing the problem that buildings which serve as landmarks on the route cannot be readily recognized. Furthermore, in the conventional navigation apparatus, a distinction cannot be readily made on the map between buildings with townpage information associated therewith (hereinafter referred to as townpage buildings) and other buildings (hereinafter referred to as ordinary buildings).
In view of the above, it is an object of the present invention to provide a stereoscopic map display method for an on-vehicle navigation apparatus, which improves visibility.
It is another object of the present invention to provide a stereoscopic map display method for an on-vehicle navigation apparatus, which readily allows distinguishing buildings with information such as townpage information associated therewith from other buildings.
To these ends, the present invention, in one aspect thereof, provides a map display method for displaying a map image on a display apparatus. The method includes the steps of changing a threshold value according to the display scale; stereoscopically displaying one or more buildings as tall as or taller than the threshold value; and monoscopically displaying one or more buildings shorter than the threshold value.
The threshold value may be increased as the contraction ratio of the map becomes larger.
The arrangement may be such that, of the one or more buildings as tall as or taller than the threshold value, only one or more buildings with particular information associated therewith are displayed stereoscopically.
The one or more buildings with particular information associated therewith may include buildings with townpage information associated therewith, including shops, companies, and/or public facilities.
Also, the arrangement may be such that, of the one or more buildings displayed stereoscopically, one or more buildings as tall as or taller than a first height are displayed as opaque images and the other buildings are displayed as transparent or semitransparent images.
Furthermore, the one or more buildings displayed semitransparently may be displayed so that roads and other buildings behind them can be recognized.
Also, one or more buildings as tall as or taller than a second height, greater than the first height, may be texture-mapped and displayed as opaque images.
The present invention, in another aspect thereof, provides a map display method for displaying a map image on a display apparatus. The method includes the acts of monoscopically displaying one or more buildings shorter than a specified threshold value; and stereoscopically displaying one or more buildings as tall as or taller than the threshold value and drawing shadows as the buildings are projected.
The arrangement may be such that, of the one or more buildings as tall as or taller than the threshold value, only buildings with particular information associated therewith are displayed stereoscopically and drawn with shadows.
Also, the one or more buildings with particular information associated therewith may include buildings with townpage information associated therewith, including shops, companies, and/or public facilities.
Furthermore, the positions of the shadows may be changed in accordance with the actual position of the sun.
The present invention, in still another aspect thereof, provides a map display apparatus. The map display apparatus includes a storage unit for storing information, including height information, regarding each of one or more buildings; a display unit, on which a map is displayed; an operation unit for selecting a display scale; and a control unit for determining the display mode of the one or more buildings in accordance with at least the height information of each of the one or more buildings and displaying a structure-shape map on the display unit. The control unit changes a threshold value in accordance with the display scale selected in the operation unit, displaying on the display unit one or more buildings as tall as or taller than the threshold value stereoscopically while displaying one or more buildings shorter than the threshold value monoscopically.
The control unit may determine the display mode based on information regarding the number of floors of the one or more buildings and a threshold value regarding the number of floors.
The arrangement may be such that the control unit stereoscopically displays, of the one or more buildings as tall as or taller than the threshold value, only one or more buildings with particular information associated therewith.
Also, the arrangement may be such that the control unit displays, of the one or more buildings displayed stereoscopically, buildings as tall as or taller than a first height as opaque images and the other buildings as transparent or semitransparent images.
Furthermore, the control unit may display roads and other buildings behind the one or more buildings displayed as semitransparent images so that the roads and other buildings can be recognized.
Also, the control unit may texture-map and display as opaque images one or more buildings as tall as or taller than a second height, greater than the first height.
The present invention, in yet another aspect thereof, provides a map display apparatus. The map display apparatus includes a storage unit for storing information, including height information, regarding each of one or more buildings; a display unit, on which a map is displayed; an operation unit for selecting a display scale; and a control unit for determining the display mode of the one or more buildings in accordance with at least the height information of each of the one or more buildings and displaying a structure-shape map on the display unit. The control unit changes a threshold value in accordance with the display scale selected in the operation unit, displaying on the display unit one or more buildings shorter than the threshold value monoscopically, while displaying one or more buildings as tall as or taller than the threshold value stereoscopically and drawing shadows as the buildings are projected.
The arrangement may be such that the control unit stereoscopically displays, of the one or more buildings as tall as or taller than the threshold value, only one or more buildings with particular information associated therewith, and draws shadows in association therewith. Also, the positions of the shadows may be changed in accordance with the actual position of the sun.
In accordance with the present invention, the number of buildings which are displayed stereoscopically can change in accordance with the display scale, maintaining visibility of the stereoscopic map. Furthermore, roads and buildings behind other buildings can be recognized, further improving the visibility of the stereoscopic map. Furthermore, a scene approximating the actual scene is produced on the map, facilitating recognition of the direction of the vehicle.